On 03/12/2013 12:46 AM, Wolfgang Hennerbichler wrote:
On 03/11/2013 11:56 PM, Josh Durgin wrote:
dd if=/dev/zero of=/bigfile bs=2M &
Serial console gets jerky, VM gets unresponsive. It doesn't crash, but
it's not 'healthy' either. CPU load isn't very high, it's in the waiting
state a lot:
Does this only happen with rbd_cache turned on? If so, it may be the
same cause as http://tracker.ceph.com/issues/3737.
Indeed it does only happen with rbd_cache turned on. Without the cache
the jerking doesn't happen, but it's slower by a factor of three (well -
we knew this before, right):
(without rbd-cache):
dd if=/dev/zero of=/bigfile bs=2M count=100
209715200 bytes (210 MB) copied, 9.32188 s, 22.5 MB/s
(with rbd-cache):
dd if=/dev/zero of=/bigfile bs=2M count=100
209715200 bytes (210 MB) copied, 3.12769 s, 67.1 MB/s
And yes, we've also seen lost packets on the network on a busy machine
with rbd_cache, so this is totally the issue in the bugtracker.
Anyone seeing this problem, could you try the wip-rbd-cache-aio branch?
Thanks,
Josh
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